The ultimate goal of this research program is to understand, in terms of the interactions of specific amino acids, the recognition byu cytotoxic T-lymphocytes (CTLs) of class I molecules encoded in the major histocompatibility complex of the mouse. Two complementary approaches will be used to create synthetic target structures for CTL recognition. First, a fused exon construct, which has recently been completed, will be used for cassette mutagenesis (in vitro gene conversion) to generate a family of mosaic Ld-Dd class I molecules and to investigate their recognition by Ld and Dd specific CTLs. This fused exon will also be used to introduced other class I-specific and even class II- specific sequences into the Ld molecule, in order to explore T lymphocyte reactivity. Second, class I-derived peptides, which bind to class I molecules,can be used to generate CTL epitopes, as described in the Progress Report, see page 25; we will determine the scope of this phenomenon. The projects outlined in this research program will lead to an in depth understanding of the important structural elements which MHC molecules must posses for T-lymphocyte recognition. This is a prerequisite for the successful manipulation of the immune response and should result in the development of molecularly rational therapies for many diverse disease such as cancer, autoimmune conditions as well as transplantation.